Counterflow of gas and particles is highly desirable in moving bed granular filters to achieve high dust removal efficiency from contaminated gas streams. In counterflows the dirty entering gas is scrubbed by the dirtiest particles and the clean exiting gas is scrubbed by the cleanest particles. However, moving bed granular filters that utilize counterflow typically have a low gas throughput to prevent bed material from leaving the filter when the minimum fluidization velocity of the granules is exceeded.
A disadvantage of the cyclonic flow of the gas is a disturbance of granules and collected dust at the interface between the gas and granular bed. Momentum transfer from the cyclonic gas flow imparts a swirling flow to the granules and collected dust, which makes the flow through the filter non-uniform and adversely imparts filtration efficiency.
The lack of durable, low-cost filters to clean high temperature gas streams is one of the primary obstacles to commercial introduction of advanced power systems based on coal and biomass. The two most promising filtration systems being investigated by government and industry are ceramic barrier filters and moving bed granular filters.
Ceramic barrier filters have several disadvantages: they must be periodically regenerated (blow back) to remove accumulated dust; they are fragile; and they are expensive.
Moving bed granular filters have been developed in several different geometries. These can be roughly characterized as parallel flow, counterflow, and crossflow filters. Parallel flow of gas and particles results in clean gas disengaging from dust-laden granules. Under these circumstances, dust can be entrained with the gas, which reduces the dust collection efficiency of the filter. Crossflow filters require very complicated tuyeres to inject dirty gas into the moving bed of granules. These are expensive and do not fully solve the dust carryover problem of gas disengagement.
Moving bed granular filters operate on the principle that a flowing bed of particles can effectively scrub particulate contaminant from a gas stream. Although very promising for achieving high filtration efficiencies, the relatively large footprint of the equipment and high throughputs of granular material as filter media are cited as drawbacks to moving bed granular filters.
It is therefore a principal object of this invention to incorporate these novel design features: A tangential gas inlet, a flow straightening section at the interface between entering gas and the granular bed, a screened gas disengagement section, and a diamond shaped insert.
These and other objects will be apparent to those skilled in the art.